The instant invention relates to a process for piecing in an open-end spinning device in which a fiber stream is produced and is deflected by means of an auxiliary suction air stream from its course to the fiber collection surface of a spinning rotor until a yarn end is fed back to the fiber collection surface of the spinning rotor. The auxiliary air suction stream is deactivated in coordination with the back-feeding of the yarn end, a negative spinning pressure is produced in the spinning rotor and the fiber stream is fed through a fiber feeding channel to the fiber collection surface of the spinning rotor where the yarn end is united with the newly fed fibers and is then drawn off through a yarn draw-off pipe as fibers are integrated into the yarn. The invention relates as well to a device to carry out this process.
According to a known process of this type (WO 86/01235), a yarn end is introduced with the assistance of a pair of feeder rollers into the yarn draw-off pipe and is then released by the pair of feeder rollers. During this introduction of the yarn end into the yarn draw-off pipe, the negative spinning pressure is switched on in the spinning rotor. In addition an auxiliary negative pressure which is applied to the opener roller housing takes effect in the yarn draw-off pipe. With the spinning rotor running, the fiber feed is then released and the fiber stream thus produced is however prevented by the auxiliary negative pressure from entering the spinning rotor. A yarn reserve is dissolved in that the yarn is thrown off from a throw-off spindle. Because of the auxiliary negative pressure taking effect through the fiber feeding channel, and because of the centrifugal force produced by the rotating spinning rotor, the yarn end which is freed by being thrown off is sucked into the spinning rotor and deposited on its fiber collection surface. In a timed synchronization therewith, the fiber stream is guided into the rotating spinning rotor by switching on the negative spinning pressure and switching off the auxiliary negative pressure, whereby the fibers are united within the spinning rotor with the yarn end which is now drawn off from the spinning rotor and is wound up on a bobbin while the fibers are continuously integrated into the yarn.
The yarn end deposited on the fiber collection surface is twisted by the rotating spinning rotor from the instant of deposit. To avoid over-twisting the yarn end, the latter may remain only for a very short time in the spinning rotor, so that also during its back-feeding to the fiber collection surface the yarn end is exposed for only a short time to this rotation effect. As the yarn is thrown off, the yarn end does reach the fiber collection surface very rapidly, but this back-feeding is undefined with respect to time, as the rapidity with which the yarn end reaches the spinning rotor varies with the yarn number, the fiber material, etc. In addition, the back-feeding of the yarn to the fiber collection surface is also influenced by the rotational position of the throw-off spindle which releases the yarn reserve. Precise timed synchronization with the release of the fiber stream is therefore not possible.